Rename test_live_block_migration to test_live_migration

These tests can actually test both block and regular live migration, so
update the filename to reflect that.

Also move test to admin, since by default migration is a admin only API call

Change-Id: Ibdae2e8ba9b537ed721bc4448d7107d3f8eaf013
diff --git a/tempest/api/compute/test_live_block_migration.py b/tempest/api/compute/admin/test_live_migration.py
similarity index 100%
rename from tempest/api/compute/test_live_block_migration.py
rename to tempest/api/compute/admin/test_live_migration.py